SOC Concrete Flashcards
- What are the raw materials in Portland cement?
Limestone Cement rock Oyster shells Marl (Lime-rich mud-lake sediment) Clay Silica Sand Iron Ore
- What is “clinkers”?
The raw material finely ground and carefully proportioned before heated to temperatures from 2000 to 3000 degrees (F) to form hard pellets called “Clinkers.” Cooled and then pulverized to a fine powder.
- What is air entrainment?
The intentional creation of tiny air bubbles in concrete
- What is the composition of concrete?
Mix of aggregates and entrained air held together by hardened paste made of cement and water
- What is the most commonly used cement by the military?
Portland cement
- What is hydration?
Hydration is the chemical reaction that occurs when Portland cement is mixed with water. Produces heat that causes expansion and contraction.
- What causes concrete to harden and what is the desired temperature?
Hydration
73 degrees
- What are the three major components of concrete?
Water
Aggregates
Portland Cement
(Coarse agg, fine agg, hydraulic cement, water, air)
- What are two types of aggregate
1) Coarse aggregate (Rock)
2) Fine aggregate (sand)
- What is aggregate?
It used as an inner filling material, made of sand and gravel. 60 to 80 percent of total concrete volume. Should be clean, round, hard, strong and durable.
- What is primary purpose of aggregates?
To gain economy
Use largest practical size to gain maximum strength
- What are the most common contaminating materials of aggregate?
Dirt, clay and salt
Most can be removed by washing with water
- What are the five types of Portland cement?
Type I (Normal Portland) Type ll (Modified) Type III (High early) Type IV (Low heat) Type V (Sulfate Resistant)
- What is the normal cure time and some uses of Type 1 Portland cement?
28 days
It used for Pavement, Sidewalks, Bridges, Reservoirs, Building and etc
- What is the normal cure time and some uses of Type 2 Portland cement?
45 days
Large super structures, large piers, heavy abutments, heavy retaining walls
- What is the normal cure time and some uses of Type 3 Portland cement?
High early -7 days
Used in cold weather and high heat
- What is the normal cure time and some uses of Type 4 Portland cement?
Low heat -90 days
Large massive structures
- What is the normal cure time and some uses of Type 5 Portland cement?
Sulfate Resistant – 60 days
Used where the soil, or water, in contact with the concrete has a high sulfate content
- What types of Portland cement are air entrained?
Types 1, 2 and 3
Aids in freeze/thaw resistance
- What does calcium chloride do to Portland cement?
It accelerates both hardening and strength gain by 2% the weight of cement. Used in temps where hydration is slow
2 hours vs 6 hours
- How does Portland cement ship?
Bags
94lb - contain one cu ft of loose measurement
Barrels
376lb = 4 bags
Rail cars
- What is warehouse pack?
Sacked cement in storage packed too tightly
- What are the types of concrete?
Reinforced
Prestressed
Precast
Lightweight
- What is reinforced concrete?
Steel rods imbedded into the concrete (strong in compression, but weak in tensile strength)
- What is prestressed concrete?
Reinforced steel or welded wire mesh that is stretched out with tension before the concrete is poured.
- What is precast concrete?
Concrete cast somewhere other than its final position
- What is benefits of lightweight concrete?
a) In dead-loads making savings in foundations and reinforcement
b) Improved thermal properties
c) Improved fire resistance
d) Savings in transporting and handling pre-cast units on site
e) Reduction on framework and propping
- What is benefits of plastic state?
a) Readily moldable
b) Changes shape slowly if forms are removed
c) Uniform
d) Workable nonsegregated
It can be cast or molded into nearly any size or shape
- What are some advantage of concrete?
a) High compressive strength
b) Can be cast, molded or shaped
c) Little maintenance
d) Economical
e) Used Universally
d) Durable
e) Strength can be pre-determined
- What are some disadvantage of concrete?
a) Low tensile strength
b) Expands and contracts
c) Shrinks when dry
d) Heavy
- What is expansion and contraction?
Chemical reaction that occurs by moisture and temperature changes
- What is the width of an expansion joint?
1/4 to 1/2 inch
- What is the difference between construction joints and expansion joints?
Construction joints (Horizontal and Vertical Keyways) are not intended to allow for movement of concrete. Expansion joints and contraction joints allow for movement.
- When can you place concrete underwater?
Placed underwater only when unavoidable.
- If concrete must be placed underwater, what should the max velocity of the current be?
10 ft per min
- When hand mixing cement, how much cement can be mixed by one man?
1 cubic yd per hour
- When hand mixing concrete the sand, gravel and cement should be dry mixed how many times before adding water?
Three times
- What is the formula for project volume (PV)?
PV = Length x Width x depth x number of structures.
• Make sure keep in feet, divide inch measurements by 12
- What is the formula for Loss Factor (LF)?
LF = PV x LF
<5400 cu ft =1.1 or > 5400 cu ft = 1.05
- What is the formula for loose volume (LV)?
LV = LF X 1.5
- What rule do you use when calculating for materials when laying concrete?
1-2-3 rule
1/6 cement, 2/6 sand, and 3/6 gravel
- What is the formula for convert cu ft to cu yrds?
Cu ft / 27 = cu yrds
- When estimating for concrete work what is the rule called?
3/2 rule
- What are forms?
Structures that hold concrete until sets, produces the desired shapes and sometimes surface finishes. Can represent up to 1/3 of concrete structure’s total cost.
- What is essential when setting up forms?
Tight
Rigid
Strong
- What materials can be used make forms?
Wood (most common and economical)
Metal
Earth
Fiber
- What are the elements of wooden forms (Concrete wall)?
Sheathing Stud Wales Strong backs Braces Shoe plates Spreaders Tie wires
- What are the elements of wooden forms (Concrete column)?
Sheathing
Batten
Yokes
Bracing
- The rate of filling should not be exceed?
4 feet per hour vertically, to avoid excessive pressure on the forms, should never be dropped from greater than 3-5 feet.
- What is screeding?
Process of stiking off the excess concrete in order to bring the surface to the right elevation
- What are techniques of finishing operation?
Floating - If smooth surface is required Troweling - smoother surface is required Brooming - If non-skid surface is required Screeding - trimming excess off top Vibration
- What determines the strength of concrete?
Ratio of cement to water, less water = stronger
- What are the rules of thumb for the maximum size aggregates should be in concrete?
The maximum size should not exceed 1/5 the minimum diameter of a wall or similar structure Not to exceed 1/3 the slab thickness Not to exceed 3⁄4 of the clear space between reinforcing bars
- Where are isolation joints used?
where a pavement joins sidewalks and building, and intersects other pavements or bridge.
- What do expansion joints do?
Permit volume change movement of a concrete structure or member.
- how deep does the land under a slab need to be moistened?
6 inches
- Slabs which will support load bearing walls must be what?
Reinforced with rebar
- What is different between construction joint and Control joint?
1) Construction joints allow the builder to continue construction process.
2) Control joint is used at finishing state of construction. A provision for volume changes at predetermined locations that prevents a concentration of crack-producing stress forces.
- What is sequence of concrete hand mixing?
a) Mix dry materials three times (sand, cement, and grave)
b) Add water to achieve desire concrete strength
- Ingredient Equation
PV = L x W x H x ( number of structure) • Keep measurement in feet Loss factor LF= PV(1.1) ( <5400 cu ft, add 10% (1.1) LF= PV(1.05) ( >5400 cu ft, add 5% (1.05) Loose Volume LV= LF X 1.5 • LV round up to whole number 1) CEMENT 1/6 X LV = bag of cement 2) SAND 2/6 X LV = CU ft 3) Gravel 3/6 x LV = CUft Water Gallons = 8 x # of bag cement
If you ordering from truck, LF = PV x (loss factor of 1.05) YDS = LF(in CU ft) / 27 Always going to be CU yard Only round at end
- Special curing techniques
1) Hot weather keep temperature below 90 F degree Loosen forms ASAP Add accelerators Remove forms (7 days)
2) Cold weather
40 degrees F or lower
Keep concrete above 70 degrees F
Add accelerators
What is the purpose of water in making concrete?
Effect hydration
Improve workability
What are the requirements for water used in concrete?
It should be free of acids, alkalis, oils, and other organic impurities (excessive sulfates)
How do you find the largest practical size for aggregate?
<1/5 minimum diameter of a wall
<1/3 slab thickness
<3/4 clear space between reinforcing bars
What are the other types of cement?
White Portland - Architectural Air entrained - freeze-thaw Oil Well - hardens at temps in deep wells Waterproofed Portland Plastic Cement
Properties of desirable concrete
Hardened Concrete (strength determined by water content: 1 bag = 2.5 gallons)
Durability
Water-tightness
Types of Foundations
Footer
Monolithic Slab
Stem Wall
Floating Slab
